1. Field of the Invention
The present invention relates to a battery use system for a portable electronic equipment and, more particularly, to a battery use system capable of prolonging a use time of a battery-driven portable electronic equipment.
2. Description of the Related Art
Conventionally, as a power supply battery used in a portable electronic equipment, a nickel-cadmium battery having a in high safety and a low internal resistance, a nickel-hydrogen battery having a larger capacity, or the like is often used. However, to use the electronic equipment for a longer time, the capacity of the power supply need to be increased. For this purpose, a battery back-up system by a primary battery as in the first prior art (to be described later), multi-stage series connection as in the second prior art, or a lithium-ion battery having a larger capacity as in the third prior art is used.
More specifically, in the first prior art, as shown in FIG. 1, a secondary battery 100 is parallelly connected between a power supply input terminal 7 and a ground terminal 8 of an electronic equipment 110 through a diode 28. A primary battery 31 is also parallelly connected between the terminals 7 and 8 through a charge preventing diode 29 and a resistor 30. Normally, the secondary battery 100 applies a power supply voltage to the electronic equipment 110 while no power is supplied from the primary battery 31 because of the function of the resistor 30. Additionally, because of the function of the charge preventing diode 29, the primary battery 31 is not charged by the secondary battery 100. When the power supply from the secondary battery 100 is stopped, the power supply for the electronic equipment 110 is backed up by the primary battery 31.
In the second prior art, as shown in FIG. 2, a number of power supply batteries are connected in series with each other to constitute a secondary battery 32. This secondary battery 32 is set to a desired voltage through a regulator 33 and parallelly connected to an electronic equipment 110, thereby increasing the capacity of the power supply.
In the third prior art, as shown in FIG. 3, a lithium-ion battery 13 whose large capacity is receiving a great deal of attention today is parallelly connected to an electronic equipment 110.
Note that, in the present invention, an unchargeable battery which is discarded after consumption is defined as a primary battery, and a chargeable battery is defined as a secondary battery.
The above prior arts have the following problems.
That is, in the first prior art, since the primary battery 31 is used, this battery is wastefully discarded after discharge. In addition, the primary battery 31 may be charged and explode due to leakage of the charge preventing diode 29.
In the second prior art, because of the simple multi-stage series connection of batteries, the number of batteries is large resulting in an increase in weight and volume of the portable electronic equipment.
In the third prior art, the lithium-ion battery has a large capacity. However, since the battery has a large internal resistance, a large voltage drop is generated upon outputting a large current. Especially in an electronic equipment for performing an intermittent operation, the operation becomes unstable, and noise is generated.